This library currently supports h2, which negotiates over TLS. However, it appears that it does not support the Upgrade negotiation of h2c, which requires a bit deeper integration with the http lib, rather than hijacking the protocol at the TLS level.

Some people seem to find TLS-less HTTP to be a controversial subject, for some peculiar reason, but it is part of the spec. I unfortunately also happened to look at this project because I needed it. Oh well.